High-energy high-capacity oscillating ball mill

ABSTRACT

The present invention concerns a high energy oscillating ball mill, useful in the preparation of nanophase materials having crystallite sizes of the order of 5 to 20 nm, with high production capacity and consisting of a grinding jar (containing, in the working conditions, the grinding balls and the materials charge to be processed) driven in an alternate regime of motion. Such a grinding jar is elastically constrained in such a way that the inertial forces originated during the oscillations are compensated.

TECHNICAL FIELD

The present invention concerns a high energy ball mill and in particularan oscillating mill having high production capacity. It is possible touse such a mill for example in the preparation of nanophase materials.

Nanophase materials are characterized by crystal sizes in the range 5 to20 nm. Such materials can be constituted by single metals, alloys,compounds or composites (for example alloy/metal-oxide,alloy/metal-carbide).

The preparation of such materials can be performed in high energy mills(high local impact energies are in fact required).

BACKGROUND ART

Conventional high energy mills include, for example: autogenousgrinders, abrasion grinders, gas jet or liquid jet disintegrators, ballanular mills, vibratory ball mills, planetary ball mills and oscillatingball mills.

For a more complete description of these mills, reference may be made to"Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd edition, vol. 21,p 132 to 161".

DE-A-3,500,211 describes a ball mill wherein a system of springscompensate the gravity forces, CA-A-1,108,574 describes a ball mill withmeans for conducting oscillation from a mechanical oscillator, U.S. Pat.No. 3,433,421 describes a vibratory mill comprising a drum mounted on ashaft driven through an orbit described by oscillative movement alongand about the major axis of said driven shaft.

In the present state of development of mills technology it is notpossible to have at the same time: 1) high impact speeds of the grindingmeans; 2) high specific pressures in the impact zones; 3) high impactfrequencies for each grinding means; and 4) high production capacity.

Existing milling systems are therefore scarcely or ill suited for thefast preparation of nanophase materials in large quantities.

SUMMARY OF THE INVENTION

It is an object of the present invention to achieve a mill in which anadvantageous combination of the above characteristics is achieved.

It is also an aim of the present invention to achieve a system for theproduction of nanophase materials powders in large quantities.

It is also a further object of the present invention to achieve the fastmilling of solids.

An advantage of the present invention is to allow the production oflarge quantities of nanophase materials for the further consolidationprocesses.

According to the present invention there is provided an oscillating millconsisting of a grinding jar (containing, in the working condition, thegrinding balls and the materials charge to be processed) driven in analternate regime of motion. Such a grinding jar is elasticallyconstrained in such a way that the inertial forces originated during theoscillations, and acting on the driving system, are compensated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following an illustrative and not limitative embodiment of theinvention is given, with the help of FIGS. 1 and 2.

The FIG. 1 shows a plan view of the grinding jar with elasticcompensation system;

the FIG. 2 shows a cross-section of FIG. 1 along the plane A--A and thepre-loading apparatus of the elastic system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1 and 2 the same part or parts performing the same functionsbear the same numbers. In FIG. 1, 1 is the elastic system for thecompensation of the inertial forces and consists of a spring of anelastomeric material. In FIG. 2, another (counteracting) spring islocated on the other side of the grinding jar which is constituted bythe following components: a top cap 2; a bottom cap 3; a lateral wall 4with provision for seals 5 with the seals 11 with the lateral coolingmantle system 6.

The cooling mantle system 6 is constituted by an internal finning (onthe side of the lateral jar wall 4) in which a cooling fluid is allowedto circulate with inlet in 7 and outlet in 8.

The seals 11 act for the cooling fluid whereas seals 5 have the purposeto allow the control of the internal jar atmosphere (vacuum, inert orreactive gases) performed by means of valve 13 passing through opening21.

In the caps 2 and 3 are located joint systems 18 by tie rods. Thegrinding jar, constituted by the above components, is placed in contactwith springs 1 by a spring pre-loading system constituted of a springhousing plate 17, pre-loading calibrated handwheel 15, bearing plate 14overturnable on the hinge 19, fastening screw 16.

The working principle of the mill is based on the drive of the setjar-springs by a ball joint 12 in alternating motion substantially alongan axis 20 with sinusoidal-like law. The lateral guiding system consistsof bearing plates 9 of guides 10 in low friction coefficient materials.The grinding jar is charged before with the material to be processed andthe grinding balls.

In a practical embodiment of the present invention: the grinding jar hasa diameter of 300 mm; charge capacity of 1 kg of material to beprocessed; motion induced by a kinematic mechanism connecting-rod crank;oscillation frequency 17 Hz; oscillation amplitude 30 mm; internal jarvolume 5000 cm³. The maximum inertial forces during the oscillation ofthe grinding jar with the total charge (materials to be processed plusgrinding balls) are of the order of 1200 kg. Such forces, which havealso a sinusoidal-like behaviour, are partially (70% or more)compensated by springs 1 (having elastic constant 40 kg/mm) in such away that the residual load on the joint 12 can be sustained along allthe oscillation cycle.

In a typical oscillating ball mill according to the present inventionhaving an internal jar volume above 200 cm³, more particularly above5000 cm³ :

(a) the motion components perpendicular to axis 20 do not exceed inamplitude the 20% of the motion components along axis 20;

(b) there is a compensation of at least the 70% of the inertial forcescomponents generated by the grinding jar 2, 3, 4 along the axis 20;

(c) the jar oscillating amplitudes along the axis 20 are greater than 20mm and jar oscillation frequencies along the axis 20 are greater than 10Hz.

In a further not limitative embodiment of the invention the grinding jaris constituted of hardened steel (components 2, 3, 4), the lateralmantle 6 is of aluminium and guides 10 are made of teflon.

It has been therefore described a preferential description of theinvention, but other variants are possible.

It is easily feasible to increase in the production capacity of the millby increasing the dimension (for example the diameter) of the grindingjar and modifying accordingly the elastic system for the compensation ofinertial forces.

It is possible, for example, to utilize an elastic system, to compensatethe inertial forces, constituted of springs made of metallic alloys orcomposite materials. Dissipative systems to compensate the inertialforces by a compressed fluid can be well utilized (such as for examplegas or oil or water shock absorbers). It is also possible to use a mixedelastic-dissipative system.

It is also possible, for example, to utilize other alternative motiondriving systems such as cams, compound levers, hydraulic or hydraulicsystems with proportional valves.

It is also possible to utilize other alternative motion driving systemsin variable regime as regarding the width/frequency of the oscillationand wave shapes.

It is possible, for example, to utilize for the guides 10 othersolutions compatible with a low friction coefficient (lubricated orself-lubricated guides, materials having low friction coefficient). Itis also possible not to utilize a guiding system, once provided alimitation of the non-axial components of the motion.

It is possible, for example, not to provide a jar cooling circuit as thejar itself could be cooled by natural convection.

It is possible, for example, to shape differently the internal jarsurfaces in order to limit the extension of preferential ball impactzones.

It is possible, for example, to increase the productivity to utilize,instead of a single jar 2, 3, 4, multiple-constrained (each other) jars.

It is also possible to utilize other pre-loading 14, 15, 16, 17, 19systems such as mechanical systems by compound lever, wedge or hydraulicjacks.

It is also possible to vary materials, shapes, sizes and proportions,all of this being possible for a person skilled in the art withoutdeparting thereby from the scope of the inventive idea of the invention.

We claim:
 1. An oscillating ball mill comprising a driving system, agrinding jar, a bearing system, and an elastic system, wherein saiddriving system and said elastic system are in direct contact with saidgrinding jar, said elastic system compensates the inertial forcesresulting from the operation of said driving system, and the grindingjar motion is substantially along an axis.
 2. The oscillating ball millaccording to claim 1, wherein the driving system moves along said axisin a sinusoidal-like manner.
 3. The oscillating ball mill according toclaim 1, further comprising a dissipative system to supplement saidelastic system in compensating said inertial forces.
 4. The oscillatingball mill according to claim 1, wherein said elastic system comprisessprings of elastomeric material.
 5. The oscillating ball mill accordingto claim 1, wherein:the motion components perpendicular to said axis donot exceed in amplitude the 20% of the motion components along saidaxis; said elastic system compensates at least 70% of said inertialforces; and the jar oscillating amplitudes along said axis are greaterthan 20 mm and jar oscillation frequencies along said axis are greaterthan 10 Hz.
 6. The oscillating ball mill according to claim 1, whereinsaid driving system is a connecting rod-crank kinetic mechanism.
 7. Theoscillating ball mill according to claim 1, having more than one jarconstrained together.
 8. The oscillating ball mill according to claim 1,wherein the jar motion is guided by guides.
 9. The oscillating ball millaccording to claim 1, wherein the internal walls of said grinding jarare shaped to limit the existence of preferential impact zones.
 10. Theoscillating ball mill according to claim 1, wherein said elastic systemis pre-loaded by a mechanical system.
 11. The oscillating ball millaccording to claim 1, wherein said grinding jar is cooled by fluidcirculation.
 12. The oscillating ball mill according to claim 1, whereinthe atmosphere in said grinding jar is controlled by at least one valvepassing through at least one opening in said jar.
 13. The oscillatingball mill according to claim 1, wherein the internal jar volume isgreater than 200 cm³.
 14. The oscillating ball mill according to claim1, wherein said elastic system comprises springs of a metallic alloy.15. The oscillating ball mill according to claim 1, wherein said elasticsystem comprises springs of a composite material.
 16. The oscillatingball mill according to claim 1, wherein said driving system is acompound lever.
 17. The oscillating ball mill according to claim 1,wherein said driving system is a hydraulic drive.
 18. The oscillatingball mill according to claim 1, wherein the internal jar volume isgreater than 5000 cm³.